Concrete slipform pavers are known. Specifically, such pavers include a xe2x80x9ctractorxe2x80x9d and a xe2x80x9cpaving kitxe2x80x9d.
Regarding the tractor, most concrete slipform pavers include a tractor, which is comprised of a rectilinear frame. This rectilinear frame has bolsters extending parallel to the direction of machine travel and cross beams extending across the paved roadway or runway. The rectilinear frame thus straddles the paved concrete path while it is paved. This frame is propelled and supported on either end by side crawler track(s). The frame supports a diesel engine driven hydraulic power unit, which supplies power to the tractor and paving kit.
The paving kit is typically suspended below the rectilinear tractor frame by mechanical means. The paving kit takes its hydraulic power from the power unit on the tractor. The tractor and paving kit comprise the slipform. This slipform passes over concrete placed in its path. The concrete is placed in a relatively even and level mass that can be either flat, super elevated (as at curves in the roadway) or crowned. During this slipform process the tractor attached paving kit spreads the concrete dumped in the path of the paver, levels and vibrates it into a semi-liquid state, then confines and finishes the concrete into a slab with an upwardly exposed and finished surface. Sideforms mounted to the side of the slipform kit confine the sides of the slab during the paving process.
The tractor typically has either two or four crawler tracks supporting and propelling the frame and attached paving kit. Other kits can be attached to these tractors such as kits for conveying and spreading concrete and trimming and spreading base materials. For the purposes of this description, we will focus on the paving kit working in conjunction with a rear mounted, dowel bar inserter kit used for slipforming a concrete slab and concurrently inserting dowel bars in the plastic concrete across the slipform paved slab.
Dowel bars, tie bars and inserters for dowel bars and tie bars on such paving machines are known. In general, dowel bars are placed parallel to the direction of machine travel and ties bars are placed across the direction of machine travel. Specifically, three types of inserters for such bars are known. First, there is the tie bar inserter for the edge of the slab. This tie bar is placed transverse to the paving direction and enables tying of sequentially placed side-by-side slabs, one to another. This type of tie bar and tie bar inserter is not of concern here.
Second, there is the tie bar inserter for placing tie bars completely within the placed slab. A placed slab might be a two or more 12xe2x80x2 (3.657 mm) wide lane being placed concurrently in one pass. These tie bars are placed in a line transverse to the direction of machine travel. These tie bars enable a joint to be subsequently cut in the middle of the slab parallel to the direction of machine travel. Expansion of the slab across the dimension of machine travel is not permitted, the two slabs are tied. This type of tie bar and dowel bar inserter is not of concern here.
Finally, and the most difficult insertion problem is the dowel bar inserter for placing dowel bars parallel to the direction of machine travel. The dowel bars are simultaneously placed in a line (or row) on what are typically 12xe2x80x3 (305 mm) centers, across the entire slab being slipformed by the paver. These dowel bars enable a joint to be subsequently cut in the slab across the direction of machine travel. The dowels provide load transfer between the adjoining panels in the direction of machine travel. The smooth dowels also allow the adjoining panels to move while the slab surfaces are kept on the same plane.
This type of dowel bar inserter presents the most difficult insertion problem in any slipform paver. Additionally, this type of dowel bar inserter requires modification to be made to the slipform paver to attach the dowel bar inserter. In addition to this, great effort is required to attach or remove the dowel bar inserter from the slipform paver. It might take an additional two days to assemble a machine with a dowel bar inserter. This great effort has limited the dowel bar inserters acceptance on smaller paving jobs. In what follows, we first discuss the most modern pavers, which have been developed. Second, we turn to the prior art problem of dowel bar insertion. Third, we set forth the mechanical problem of attachment and removal of dowel bar inserters to known pavers, including the pavers summarized above.
In Guntert et al U.S. Pat. No. 5,590,977 issued Jan. 7, 1997, entitled Four Track Paving Machine and Process of Transport we have disclosed a portable slip form paver that used telescoping members in the direction of machine travel. A four-track paver is disclosed having a frame, which telescopes for transport to reduce the dimension of the machine in the direction of paving machine travel. A rectilinear tractor frame is provided. The frame includes four crawler tracks, one connected to each corner of the frame via a side bolster. The crawler tracks are directly supported on a hydraulic cylinder and mounted for pivotal movement about the vertical axis of the hydraulic cylinder. The frame telescopes at side bolsters between the leading and trailing crawler tracks at the sides of the machine. When expanded, the paving machine has the full dimension required for paving. When contracted, the paving machine has a profile allowing convenient transport. Most importantly, such expansion and contraction of the machine in the direction of paving travel does not require substantial paver or paver kit disassembly. As a consequence, a convenient method of loading and off loading to a hauling flatbed trailer exists. With the frame contracted at the side bolsters and the tracks pivoted parallel to the pavement spanning dimension of the frame, both frame and paving kit are elevated and a transporting flatbed trailer moved under the paver. Supports are installed to relieve the slipform paving kit from the full weight of the tractor frame, and the tracks lifted. There results a four track paver profile transportable within a maximum width envelope which can be legally transported on the highway without a pilot car (in the U.S.A. this is this is 12xe2x80x2 or (3.657M.) This patent is incorporated by reference to this disclosure as if set forth in full.
In Guntert et al U.S. Pat. No. 5,615,972 issued Apr. 1, 1997 entitled Paving Machine with Extended Telescoping Members (see also U.S. Pat. No. 5,647,688) we have disclosed a portable slip form paver having an extendable width. A conventional telescoping frame on a paving tractor is provided with fixed frame cross beam extension members for insertion to and attachment with a telescoping frame member. The conventional telescoping frame includes paired forward and paired rear side-by-side female tube members. Each forward and rear tube member conventionally acts for the telescoping support of male extension members which attach directly to the side bolster, which in turn attaches to the hydraulic jacking columns and crawlers. Within the limits of expansion, the male extension members co-acting with clamps acting through the female tube members provide for both movement of the point of crawler support and expansion of the paving width of the tractor frame. Into this combination, extenders are added for attachment to the supported end of the male extension members interior of the female telescoping members. During frame width expansion, the male telescoping members are expanded to register their ends interior of the female telescoping members to attachment access ports in the female telescoping member. The extenders are inserted, supported, and registered at complimentary attachment apertures with attachment to the male telescoping members taking place. Once attachment has occurred, further extension of the male telescoping members occurs. A simple system of pinned cross bracing reinforces the extended frame with relatively light bracing members. When the telescoping members at both sides of the frame are provided with the extenders to extend the telescoping span of the paver, a tractor of greater expansion and range of expansion capability is provided. This width expansion obviates the need for fixed frame extensions, and permits frame expansion without heavy lifting equipment. This patent is incorporated by reference to this disclosure as if set forth in full.
Machines built to the specification of the above referenced patents require dowel bar inserters from time to time. Regarding such dowel bar insertion, the dowel bars must be placed parallel to the direction of machine travel. A line of dowel bars must be simultaneously inserted across the slab being formed. Typically, 12 to 34 or more such dowel bars can be inserted depending upon the width of pavement being paved. Center to center spacing of insertion between the dowel bars can vary. Variation can occur from about 12 inches (305 mm) on typical highway paving up to 18 inches (457 mm) for certain airport runways, aprons and taxiways. All such dowel bars must be inserted simultaneously by a mechanism, which remains stationary with respect to the plastic concrete slab being continuously formed. Thus, the dowel bar inserter must be on rails, which permit dowel bar inserter travel in the direction of concrete placement by the machine.
In U.S. patent application Ser. No. 09/411,744 filed Oct. 1, 1999 entitled Detachable Dowel Bar Inserter Kit for Portable SlipForm by the inventors herein we set forth a dowel bar inserter kit which attaches as unit to the rear of a paver. In a companion U.S. patent application Ser. No. 09/411744 filed Oct. 1, 1999 entitled Dowel Bar Inserter Kit Having Chain Feeder by the inventors herein, we stress the chain feeder used here in the preferred embodiment. In this Application, we address the unique paver kit configuration required by a so-called xe2x80x9ccrowned slab.xe2x80x9d
Placement of dowel bar inserters on existing pavers has also caused difficulty. To place such inserters on a conventional paver, substantial machine disassembly and modification must occur. First, the trailing finishing pan must be removed. Second, the conventional bolsters must be modified and extensions added to allow room in front of the rear crawler track to make room for the dowel bar inserter to work. These bolster extensions also support the dowel bar inserter kit. Third, because the rear crawler tracks have been moved back, a cross-beam must be added between the rear bolsters to prevent the extended bolsters from twisting under load. Fourth, an optional spreader plow for the correcting beam must be added. Fifth, an oscillating correcting beamxe2x80x94the beam that establishes the final slab grade from the paver, after the dowel bar inserter inserts the barsxe2x80x94must be added. Thereafter, the trailing finishing pan is reattached behind the correcting beam. To fit these required pieces of the dowel bar inserter between the rear of the slipform conforming pan and ahead of the rear crawler track can increase the center to center distance between the front and rear crawler tracks by as much as 20xe2x80x2 (6.10M). The dowel bar inserter and its related attachments also necessitates two additional trucks to haul it.
This process of attachment of dowel bar inserters is sufficiently complex, that for relatively small paving jobs, dowel bar inserters are not used because of the high mobilization cost. Instead, such dowel bars are tied together and support on xe2x80x9cbasketsxe2x80x9d or xe2x80x9cchairsxe2x80x9d and secured to the subgrade ahead of the slipform. The baskets hold the dowels in position at the center of the slab. In order to deliver concrete in front of the slipform paver, an additional machine(s) (concrete placer spreader(s)) must be employed to receive concrete from the side of the pavement then dump and spread it in front of the paver. These dowel baskets assemblies are significantly more expensive than loose dowels and require additional machinery to deliver the concrete across the front of the slipform and significant labor to install However, the extra mobilization and transport cost of a paver with a dowel bar inserter outweighs this extra cost on a small job.
We have largely solved the above problems with the disclosures referenced above. However, there remains the problem of the so-called xe2x80x9ccrowned slab.xe2x80x9d
It is common to build a xe2x80x9ccrownxe2x80x9d in continuously placed slabs. The xe2x80x9ccrownxe2x80x9d is the elevated center surface of a slab (sometimes referred to a xe2x80x9croof topxe2x80x9d profile) which enables water falling on the central portion of the slab to run to the either side of the slab. This theoretically enhances drainage. Unfortunately, where slabs have such xe2x80x9ccrownsxe2x80x9d, this complicates the placement of dowel bars using automatic dowel bar inserters mounted of the back and behind the paving kit of the slipform paver.
Regarding such a complication, automatic dowel bar inserters have their slab confining pans configured with closely spaced apertures formed between two lane spacer pans, through which dowel bars are inserted. Typically, the dowel bars are first distributed across the confining pan. Just prior to insertion the dowel bars are dropped on the recently slipformed slab at the apertures. At this point the dowels are vibrated into the slab by vibrating inserters in combination with light hydraulic pressure - with two sets of such inserter forks pushing each dowel bar into place with respect to the pan. If the inserter forks are at an angle during dowel bar insertion or not properly centered on the apertures, it is possible for the inserter forks to come into contact and interfere with the sides of the dowel bar lane spacer pans (dowel bar insertion apertures).
At the same time, uniformity of dowel bar placement with respect to the concrete slab surface is desired. It is preferred that each dowel bar be placed at a uniform depth with respect to the top surface of the slab. If the dowel bars are placed at varying depths in the slab, this placement can fall outside of the job specifications. Uniform dowel depth is important for the reasons that uniform load transfer between discrete slabs across expansion joints may not occur.
Another problem with dowel bar insertion is displacement of the plastic slab from the shape of the slipformed as it leaves the paver. Assuming that dowel bars are vibrated and inserted into a slab, the fluidized the concrete around the placed dowel bar. And when the concrete is fluidized and the mass of an additional dowel bar added to the slab, concrete becomes displaced. The displaced concrete mass must subsequently be xe2x80x9crefinishedxe2x80x9d to form an acceptable pavement surface.
In our preferred method of placing dowel bars, we place such bars through dowel bar apertures (defined between the dowel bar lane spacer pans) in a dowel bar inserter pan. It will be understood that the dowel bar inserter pan typically floats on the newly placed concrete. When a dowel bar is inserted through dowel bar apertures in a dowel bar inserter pan, slab displacement due to dowel bar insertion is confined and minimized.
The use of dowel bar inserters in combination with a dowel bar insertion pan having dowel bar insertion apertures presents another difficulty. It is necessary to keep the inserter support beam, on which the inserter fork assemblies are mounted centered in respect to the dowel bar inserter pan apertures. Such centering must occur without adversely affecting the pressure or load on the dowel bar inserter pan that floats on the plastic concrete.
In what follows, it will be seen that we have designed a dowel bar inserter kit. This dowel bar inserter kit enables dowel bars to be placed to a xe2x80x9ccrownedxe2x80x9d slab through a dowel bar inserter pan which in effects xe2x80x9cfloatsxe2x80x9d on the surface of the concrete. Inserting occurs through apertures in the dowel bar insertion pan while the pan confines at least some of the resultant expansion of the concrete due to the insertion of the dowel bars. Most importantly, the insertion of the dowel bars does not appreciably change the buoyant forces on the dowel bar inserter pan. As will be seen, this seemingly simple problem has a complex solution.
A paver is provided with a removable dowel bar inserter kit adapted for the placement of dowel bars in a slab provided with or without a crown. The paver has a propelling apparatus for moving along a paving path. A frame is supported from the propelling apparatus and includes paver bolsters extending parallel to the paving path and cross beams extending across the paving path. The suspended slipform paving kit is attached to the paver frame for receiving concrete placed on the paving path and slipforming the plastic concrete into a continuous slab on the paving path. The paving kit as suspended from the paver gives the slab its shape. This shape can be flat or crowned. When, the slab is paved with a crown, the problem solved by this invention arises.
In our improved embodiment, a dowel bar inserter kit attaches to the paver frame at four flanges. This dowel bar inserter kit has a dowel bar inserter pan defining dowel bar inserter apertures. Additionally, this dowel bar inserter kit includes dowel bar inserter assemblies. These inserters have forks which extend through the dowel bar insertion apertures in the dowel bar insertion pan. Simply stated, dowel bars are placed on the recently formed plastic slab through the dowel bar insertion apertures. As known in the prior art, the dowel bar inserters push the placed dowel bars and vibrate the placed dowel bars. As pushed and vibrated, the dowel bars are imbedded into the slab. This disclosure is directed to enabling this process to occur when a slab is crowned.
When the paver kit is attached to the paver, two lateral supportbeams extending away from the paver frame in the direction of machine travel. The two carriages are on opposite sides of the dowel bar inserter kit, and ride on the lateral support beams, with one carriage on each beam. The movement of the carriages on the lateral support beams occurs synchronously on both sides of the paving kit. The carriages travel on the beams but remain stationary with respect to the recently placed plastic slab during dowel bar insertion. The two carriages simultaneously retract to the paver frame on the lateral supporting beams at the conclusion of each dowel bar insertion cycle.
The carriages together provide four discrete functions. First, the carriages vertically support a dowel bar inserter pan to the paver through telescoping tubes and hand winches so that the buoyant force of the dowel bar inserter pan together with its alignment to and suspension from the paver can be adjustably maintained. Second, the carriages adjustably suspend an inserter beam with respect to the paver to allow a plurality of dowel bar inserter fork assemblies suspended from the support beam to place dowel bars into a continuous slab without changing force on the buoyantly supported dowel bar inserter pan. Third, the carriages provide vertical members with respect to the frame of the paver which enable side to side, fore and aft, and vertical reference of the support beam with respect to the paver frame during its required up and down inserting movement. Fourth, the carriages enable side to side, and fore and aft centering of the dowel bar inserter pan at their edges adjacent the carriages.
The suspended dowel bar inserter pan is required to crown corresponding to any crown placed in the continuous slab by the paving kit of the paver. Remembering that the dowel bar inserter pan is supported from the carriages on either side of the paver, hydraulic crowning cylinders are provided in the center of the dowel bar inserter pan. These cylinders expand to crown the dowel bar inserter pan responsive to a sensor taking reference from the corresponding crown on the paving kit of the paver. Thus the dowel bar inserter pan can be crowned to match the slab crown without requiring support from the central portion of the paver.
It is required that the insertion beam for the dowel bar inserters be centered with respect to the dowel bar insertion pan. When the insertion beam is horizontal and centered, the insertion forks for the dowel bars avoid interference with the narrow openings in the dowel bar inserter pan through which the dowel bars are introduced to the slab. However, the insertion beam must xe2x80x9ccrownxe2x80x9d in conformance with the corresponding xe2x80x9ccrownxe2x80x9d on the dowel bar inserter pan at the end of the dowel bar insertion cycle. Accordingly, central vertical telescoping tubes extend between the insertion beam at an upper end and a pin to the dowel bar inserter pan at a lower end to maintain centering and to permit insertion of all dowel bars to their specified depth. These central telescoping tubes must be maintained vertical.
The central telescoping tube attached to the insertion beam is provided with a dynamic xe2x80x9cA-framexe2x80x9d linkage to maintain verticality with respect to the frame of the paver. This central telescoping tube attached to the insertion beam imparts centering to the complimentary central telescoping beam attached to the central xe2x80x9ccrowningxe2x80x9d portion of the dowel bar inserter pan.
Regarding the central telescoping beam attached to the insertion beam, two links attach to the insertion beam equidistant from a central insertion beam hinge. The central insertion beam hinge permits insertion beam crowning; these links form the sides of the dynamic xe2x80x9cA-frame.xe2x80x9d The links are pinned at top of the dynamic xe2x80x9cA-framexe2x80x9d to the top of the telescoping tube from the insertion beam to provide a first vertical reference point to the telescoping beam. A second vertical reference point is supplied to the central telescoping beam attached to the insertion beam by rollers attached to the insertion beam. Thus, even when the insertion beam crowns as it moves with respect to the dowel bar inserter pan, a vertical telescoping tube extending from the insertion beam is provided with a vertical reference with respect to the paver.
Secondly, a complimentary central telescoping tube is pinned centrally of the dowel bar inserter pan at its lower end. This complimentary central telescoping tube is received through a roller arrangement in sliding engagement with the upper central telescoping tube from the insertion beam. Consequently, as the insertion beam moves towards and away from the dowel bar inserter pan, the insertion beam is centered with respect to the dowel bar inserter pan. Likewise, and because of the roller arrangement, such movement occurs without appreciably changing the loading on the dowel bar inserter pan.
When it is necessary to crown the dowel bar inserter pan, the insertion beam and suspended the dowel bar inserter assemblies are disposed in a horizontal disposition overlying the crowned dowel bar inserter pan. This enables the dowel bar inserter assemblies to precisely penetrate the apertures for insertion of dowel bars through the dowel bar inserter pan openings, as the dowel bar inserter both floats and is supported at its ends with respect to the recently formed and plastic concrete slab.
Because the pan is crowned and insertion beam is disposed horizontally during the initial dowel bar insertion process, the first inserter fork on either side of the crown will reach their final insertion depth first. This will not be true for the inserters at either extreme end of the dowel bar inserter beam. These inserters will only partially penetrate to their full depth.
When the dowel bar inserter beam effectively reaches full penetration of the inserters that are central to the dowel bar inserter pan, the dowel bar inserter beam is crowned by hydraulic cylinders to match the crown of the dowel bar inserter pan. This causes the inserters at each extreme end of the insertion beam to register to the dowel bar inserter apertures on the dowel bar inserter pan. At the same time, the insertion beam remains centered with respect to the dowel bar inserter pan. Full penetration of the dowel bars across the xe2x80x9ccrowned slabxe2x80x9d is assured.
In removal of the dowel bar inserters, the sequence is reversed. The dowel bar inserter beam is first moved to the horizontal disposition. It is thereafter retracted so that the individual inserter forks clear the dowel bar insertion apertures in the dowel bar insertion pan. Thereafter, the dowel bar inserter pan is retracted to the paver in the direction of paver movement with the supporting carriages moving on the lateral support beam. Repeating of the cycle occurs until paving is completed.